1. Field of the Invention
The present invention relates to an optical information storage medium, and more particularly, to an optical information storage medium in which a track pitch in all or a portion of a lead-in area is different from a track pitch in remaining areas of the optical information storage medium so that the reliability of reproduction of important optical information storage medium-related information can be improved.
2. Description of the Related Art
Optical discs are generally used as information storage media of optical pickup devices, which record information on and/or reproduce information from the optical discs without contacting the optical discs. Optical discs are classified as either compact discs (CDs) or digital versatile discs (DVDs) according to their information recording capacity. CDs and DVDs further include 650 MB CD-Rs, CD-RWs, 4.7 GB DVD+RWs, DVD-random access memories (DVD-RAMs), DVD-R, DVD-rewritables (DVD-RWs), and so forth. Read-only discs include 650 MB CDs, 4.7 GB DVD-ROMs, and the like. Furthermore, high-density digital versatile discs (HD-DVDs) have been developed which have a recording capacity of 20 GB or more.
Various methods of increasing the recording capacity of optical discs have been studied. One method of increasing the recording capacity is to reduce a size of an optical spot focused on an optical disc. To reduce the size of the optical spot, the wavelength of a laser light source should be shortened or a numerical aperture (NA) of an objective lens should be increased. Further, the track pitch of the optical disc should be reduced. The track pitch refers to a minimum distance measured from a central line of one track to a central line of an adjacent track.
FIG. 1 illustrates the structure of a conventional DVD-ROM 110. The DVD-ROM 110 includes a user data area 105 in which user data is recorded. A lead-in area 100 is formed inside the user data area 105. A lead-out area 110 is formed outside the user data area 105. Data is recorded as dots in the lead-in area 100, the user data area 105, and the lead-out area 110. Also, the track pitch is 0.74 μm in the lead-in area 100, the user data area 105, and the lead-out area 110.
The track pitch tends to be reduced when increasing the recording capacity. However, since an optical spot focused on a track may reach an adjacent track, the possibility that cross-talk will occur becomes high as the track pitch is reduced. If cross-talk occurs, an abnormal reproduction signal is output. Thus, as the track pitch is reduced, there is an increase in abnormal reproduction of information.
In particular, if information is abnormally reproduced from an area in which is recorded important information in recording and/or reproducing data, this abnormal reproduction may gravely affect a recording and/or reproduction efficiency of a disc. Accordingly, the track pitch is required to be adjusted in accordance with an increase in the recording capacity of a storage medium and the importance of data.